Insulating body for radio apparatus



March 19, 1935. s. M. KAPLAN INSULATING BQDY FOR RADIO APPARATUS Filed Oct. 31, 1931 n a P V W m m M e m u H m a B r S Patented Mar. 19, 1935 UNITED STATES PATENT OFFICE Samuel M. Kaplan,

Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application October 31, 1931, Serial No. 572,284

2 Claims. (01. 91-68) My invention relates to radio apparatus and more particularly to insulating support means employed therein for electrical elements of the apparatus.

In the construction of radio apparatus the advantages of using strong and durable insulating supporting material such as porcelain is well recognized, particularly in apparatus such as electrical coupling units for amplifiers in which tuning condenser elements, for example, are preferably mounted directly on the supporting material. It will be seen that in units for intermediate frequency amplifiers of superheterodyne receivers, it is highly essential that the condensers or other electrical tuning elements be mounted upon a support that will not subsequently warp or otherwise change its physical contour over long periods of use and thereby affect the circuit tuning characteristics appreciably.

The desirable insulating and dielectric properties of porcelain have also been recognized and have been taken advantage of in radio circuits requiring the use of stable low-loss material, particularly in the case of superheterodyne receivers where, in the above mentioned coupling units, it is customary to mount the electrical elements of each coupling unit close together and all in a small, compact unit. It has, however, been recognized that an inherent disadvantage of unglazed ceramic material such as porcelain resides in the fact that in its usual porous form it may absorb moisture or other vapors, as from the atmosphere. This often results in increasing the losses in theradio apparatus wherehigh frequency conducting parts are supported by porcelain and has generally contributed to unsatisfactory behavior of such material when used for radio purposes.

In the manufacture of such-ceramic material for the foregoing purpose, trouble from porosity has been experienced because of the difliculty in the control of the material, during heat treatment, thus necessitating extra supervision and testing facilities to guard against the occurrence of poor material. While a high grade of substantially'non-porous ceramic material for electrical insulating and supporting purposes may be made in accordance with a special process, the cost of manufacture is relatively high, and even with special precautions it may not always be of a uniform nature in quantity production.

Various attempts have been made in the past to treat ceramic material such as porcelain, for example, in such manner as to render it imper vious to moisture, as well as to provide a surface cases render the panel that does not readily gather and hold dust and foreign particles.

Numerous well known impregnating materials such as lacquer, wax, and special varnishes have been tried and tested, but in each instance there has been some serious objection. For example, in the case of insulating lacquer containing a volatile thinner it has been found that the evaporation of the thinner leaves small holes in the coating, thereby rendering the coating imperfect.

The same observation has been made with varnish and, in addition, the latter required an unusually long time to dry. In the case ofwax it was found that the coating was greasy and readily picked up dirt.' It was also found that glazing the surface of a porcelain panel did not in many impervious to moisture absorption.

Accordingly, an object of my invention is to provide a method and means for rendering porous or other absorbent insulating material, particularly ceramic material, impervious to absorption of moisture and to make it less subject to the collection of surface coatings of dust and foreign particles, while preserving the insulating properties of the material.

In accordance with my invention, I have produced a smooth, coherent, and protective coating, having a hard finish, on the surface of a body of ceramic material for sealing up the pores of the material to prevent moisture or vapors from entering the body of the material.

Further in accordance with my invention, I have provided a quick and easy method for quantity production of treating the surface of ceramic insulating material, that may be in the form of an inexpensive and low grade porcelain, to render the material impervious to moisture or vapor absorption while preserving the superior insulation low-loss characteristics of the porcelain.

Still further in accordance with my invention, I have found that numerous samples of unglazed porcelain treated with a drying oil, preferably linseed oil, raw or boiled, by the process hereinafter described, show no instability or increased dielectric loss after subjection to rigorous humidity tests or high temperature conditions, or both, and the finished product is unusually uniform in production in large quantities.

The nature of the invention may be more readily understood by reference to the accompanying drawing, in which Fig. 1 shows a view, in perspective, of an intermediate frequency coupling unit embodying the invention and adapted to be used in a superheterodyne receiving circuit, and Fig. 2 is a plan view of an insulating support element shown in Fig. 1.

In the drawing, a panel or base of ceramic insulation material 1 has mounted thereon, by means of a bracket 3 and wooden core 5, primary and secondary coils 7 and 9 respectively. A pair of semi-adjustable turning condensers 11 and 13 for tuning the respective coils '7 and 9 are mounted side by side upon the panel and secured thereto by means of eyelets 15 and 17 with the condenser parts closely spaced. A, plurality of spaced holes, indicated at 15 and 17', for the eyelets, are provided in the. porcelain panel, shown more clearly in Fig. 2, that serves to illustrate the close relation of the holes and hence the elements of the radio apparatus.

According to my invention the stability and uniformity of the insulating support 1 is improved by surface impregnation with a drying oil after having expelled all moisture by baking, and after excess oil has been removed the panel 1 is again baked to facilitate the polymerization and/or oxidation of the oil. The following procedure may be given as an example of a specific application of the method I have successfully employed.

l. The panel is baked in air for two hours at 115 C.

' 2. It is immediately thereafter impregnated in boiled linseed oil for approximately thirty minutes at a temperature of 110 C.

3. The panel, soon after the impregnation, is then washed free of excess material by dipping in a solvent such as xylol for about fifteen to high degree of temperature without efiect upon the impregnating material. The surface has a superficial thin coating of the impregnating material. However, it has been found that if this coating is broken or scraped off there remains sufiicient impregnating material in the pores of the surface to efiectively prevent penetration of moisture, etc.

One of the advantages of a. drying oil such as linseed oil is that is polymerizes, and the treatment does not involve the evaporation of a carelectrical apparatus, comprising a body of porous rier. This permits of a quick drying process, resulting in a surface having the above mentioned desirable characteristics. It has also been found that a coating that is thin and free from roughness or unevenness greatly facilitates mounting of the electrical elements. Other species of drying oil that have been found to be satisfactory for the purposes of my invention include perilla and China-wood oil.

By the term drying oil is meantone that depends substantially upon oxidation and/or polymerization for its transformation from a liquid state to its final condition as a protective coating. Tl e rate of oxidation and polymerization is, of course, a function of the temperature.

It is desirable in the above process that the coating material should be readily fiuid at the temperature used in the impregnation process, although it is not desirable that the material be so thin that it shall penetrate deeply into the body of the material. It is desirable that the coating material shall penetrate only a small distance in the surface because of the fact that the coating material, such as linseed oil, has high dielecric properties, and if it were distributed throughout the body of the ceramic material the dielectric losses would be thereby substantially inincreased. For the purpose, therefore, of preserving the low-loss characteristics of the insulating material used for radio purposes, it is desirable that the interior of the insulation material be dry and free from high dielectric substances.

Actual tests have shown that the coating material used in my above process penetrates only a small distance below the surface, or in other words, fills up the external pores, thus requiring only a small amount of drying oil.

While the coating material used in carrying out my invention is constituted substantially by a drying oil, as above disclosed, and contains little if any other substance that is volatile at ordinary temperatures, it may, if desired, have constituent substances therein adapted to improve the appearance and the physical or chemical resistance to external influences.

As a result of my invention it has been found possible to use low grade and inexpensive porcelain for radio apparatus employing high frequency currents and, by means of my process, to render this material stable and uniform in its insulating properties and particularly adapted V for large quantity production.

Although I have above disclosed the application of my invention .to a particular piece of electrical apparatus, it is obvious to one skilled in the art that it would also have utility in connection with insulation material for other purposes such as, for example, low-loss sockets for vacuum tubes, and the like.

I claim as my invention:

1. An insulating support for radio frequency ceramic material having a surface coating of a polymerized drying oil, said coating penetrating only ashort distance into. the surface of said support.

2. An insulating support for radio frequency electrical apparatus, comprising a body of porous ceramic material having a surface coating of polymerized linseed oil, said coating penetrating only a short distance into the surface of said support.

SAMUEL M. KAPLAN. 

